A large panel of monoclonal antibody reagents (191) were obtained from the B cell study section of the Fourth International Leukocyte Differentiation Conference. Using flow cytometry the percent positive cells and mean channel fluorescence were determined on purified B cell preparations from five normal individuals and five patients with B-CLL. After determining the average mean channel fluorescence and the average percent positive cells for the B-CLL and the normal B-PBL preparations, a combined ratio and difference analysis was performed for each monoclonal antibody reactivity. This analysis confirmed the intense expression of CD19, CD20, CD23 and CD24 antigens. In addition, three new clustered and three new unclustered antigens are also preferentially expressed on the B-CLL lymphocyte. Cluster analysis of these differences suggest at least three overlapping immunophenotypic subpopulations composed of CD19, CD20, CD21, CD22, CD23, CD24, CD75, CD76, and CD78. We will use this information to interpret 2D-SDS-PAGE gels and substractive cDNA libraries of normal and malignant B cells. A flow cytometric analysis of five B cell chronic lymphocytic leukemic (B-CLL) cell lines. This revealed a significant decrease in the expression of CD19, CD21, CD22, CD37 and CD73 on B-CLL lines while CD38, CD71, CD74, CD75 and CD76 are increased. Although EBV immortalization of B-CLL lymphocytes is rare, the leukemic immunophenotype has probably persevered.